Data storage device attenuating interference from first spiral track when reading second spiral track

ABSTRACT

A data storage device is disclosed comprising a disk surface comprising a first spiral track at least partially overwritten by a second spiral track, and a head actuated over the disk surface based on the second spiral track. The first spiral track comprises a periodic pattern written at a first frequency, and the second spiral track comprises a periodic pattern written at a second frequency different from the first frequency.

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/260,503, filed on Apr. 24, 2014, entitled “DATA STORAGEDEVICE READING FIRST SPIRAL TRACK WHILE SIMULTANEOUSLY WRITING SECONDSPIRAL TRACK” to Charles A. Park et al., the disclosure of which isincorporated herein by reference.

BACKGROUND

When manufacturing a disk drive, concentric servo sectors 6 ₀-6 _(N) arewritten to a disk 2 which define a plurality of radially-spaced,concentric servo tracks 6 as shown in the prior art disk format ofFIG. 1. A plurality of concentric data tracks are defined relative tothe servo tracks 4, wherein the data tracks may have the same or adifferent radial density (tracks per inch (TPI)) than the servo tracks4. Each servo sector (e.g., servo sector 6 ₄) comprises a preamble 8 forsynchronizing gain control and timing recovery, a sync mark 10 forsynchronizing to a data field 12 comprising coarse head positioninginformation such as a track number, and servo bursts 14 which providefine head positioning information. The coarse head position informationis processed to position a head over a target data track during a seekoperation, and the servo bursts 14 are processed to maintain the headover a centerline of the target data track while writing or reading dataduring a tracking operation.

In the past, external servo writers have been used to write theconcentric servo sectors 2 ₀-2 _(N) to the disk surface duringmanufacturing. External servo writers employ extremely accurate headpositioning mechanics, such as a laser interferometer, to ensure theconcentric servo sectors 2 ₀-2 _(N) are written at the proper radiallocation from the outer diameter of the disk to the inner diameter ofthe disk. However, external servo writers are expensive and require aclean room environment so that a head positioning pin can be insertedinto the head disk assembly (HDA) without contaminating the disk. Thus,external servo writers have become an expensive bottleneck in the diskdrive manufacturing process.

The prior art has suggested various “self-servo” writing methods whereinthe internal electronics of the disk drive are used to write theconcentric servo sectors independent of an external servo writer. Forexample, a known technique for self-servo writing a disk drive is tofirst write a plurality of spiral tracks to the disk, and then to servoon the spiral tracks while writing a plurality of servo sectors thatdefine concentric servo tracks such as shown in FIG. 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servotracks defined by servo sectors.

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a head actuated over a disksurface.

FIG. 2B is a flow diagram according to an embodiment wherein whilereading a first spiral track on the disk surface a second spiral trackis simultaneously written on the disk surface.

FIG. 2C illustrates the writing of a second spiral track whilesimultaneous reading a first spiral track according to an embodiment,wherein the second spiral track is written in an opposite radialdirection as the first spiral track.

FIG. 3 illustrates the writing of a second spiral track whilesimultaneous reading a first spiral track according to an embodiment,wherein the second spiral track is written in the same radial directionas the first spiral track.

FIG. 4A illustrates an embodiment wherein the first spiral trackcomprises a periodic pattern written at a first frequency, and thesecond spiral track comprises a periodic pattern written at a secondfrequency different from the first frequency.

FIG. 4B shows an embodiment wherein a read signal generated whilereading the first spiral track is bandpass filtered based on thefrequency of the first spiral track to attenuate crosstalk caused bysimultaneously writing the second spiral track on the disk surface atthe second frequency.

FIG. 5A shows a data storage device in the form of a disk drivecomprising a head actuated over a disk surface comprising a first spiraltrack at least partially overwritten by a second spiral track.

FIG. 5B is a flow diagram according to an embodiment wherein the head isservoed over the disk surface based on the second spiral track.

FIG. 5C illustrates an embodiment wherein the read element of the headpasses over the second spiral track as well as part of the first spiraltrack.

FIG. 6 illustrates an embodiment wherein a ratio of frequencies betweenthe first and second spiral tracks attenuates interference from thefirst spiral track when demodulating the read signal generated whilereading the second spiral track.

FIG. 7 shows an embodiment wherein the read signal is filtered with abandpass filter to attenuate interference from the first spiral track.

FIG. 8A shows an embodiment wherein sync marks in the first spiral trackmay interfere with the spectral signature of the second spiral track.

FIG. 8B shows an embodiment wherein the first spiral track consistsprimarily of a periodic pattern without sync marks, whereas the secondspiral track comprises a periodic pattern with sync marks.

FIG. 8C shows an embodiment wherein recording the first spiral trackswithout sync marks removes the interference from the spectral signatureof the second spiral track as compared to FIG. 8A.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a disk surface 16 comprising afirst spiral track 18, and a head 20 actuated over the disk surface 16.The disk drive further comprises control circuitry 22 configured toexecute the flow diagram of FIG. 2B, wherein while reading the firstspiral track 18 a second spiral track 24 is simultaneously written onthe disk surface (block 25).

In one embodiment, the first spiral track 18 may be considered a“bootstrap” spiral track from which the head 20 may be servoed in orderto write the second spiral track 24 which may be considered a servospiral track. In one embodiment, the disk surface 16 may comprise aplurality of bootstrap spiral tracks which may be read in order to writea plurality of servo spiral tracks. The servo spiral tracks may then beprocessed in order to servo the head 20 radially over the disk surface16 in order to write servo sectors that define concentric servo tracks.In another embodiment, the servo spiral tracks may be used as a finalservo pattern for servoing the head during normal access operationswithout needing to write servo sectors to the disk surface.

In one embodiment, the first spiral track 18 (as well as other similarspiral tracks if needed) may be self-written to the disk surface 16 bythe control circuitry 22 internal to the disk drive. An exampleembodiment for self-writing spiral tracks is disclosed in U.S. Pat. No.8,634,283 entitled “DISK DRIVE PERFORMING IN-DRIVE SPIRAL TRACK WRITING”the disclosure of which is incorporated herein by reference. In anotherembodiment, the first spiral track 18 (e.g., bootstrap spiral track) maybe written to the disk surface 16 using an external servo writer priorto installing the disk into the disk drive.

FIGS. 2A and 2C illustrate an example embodiment wherein the secondspiral track 24 is written in an opposite radial direction as the firstspiral track 18. That is, the first spiral track 18 is written from theinner diameter (ID) of the disk surface 16 toward the outer diameter(OD) of the disk surface 16, and the second spiral track 24 is writtenfrom the OD to the ID of the disk surface 16. FIG. 2C also illustratesan embodiment wherein the head 20 comprises a read element 26 that isoffset circumferentially from a write element 28 by a reader/writer gap.Accordingly in this embodiment while writing the second spiral track 24the read element 26 travels along trajectory 30A and reaches the firstspiral track 18 before the write element 28 overwrites the first spiraltrack 18 while travelling along trajectory 30B. In this manner, even ifthe read element 26 and the write element 28 are aligned so as to bothtravel along trajectory 30B, the read element 26 reads the first spiraltrack 18 before it is overwritten by the write element 28.

In another embodiment illustrated in FIG. 3, the second spiral track 32is written in the same radial direction as the first spiral track 34(e.g., from the OD to the ID). In this embodiment, the second spiraltrack 32 is written at a different radial velocity than the first spiraltrack 34 such that the slope of the second spiral track 32 is differentfrom the slope of the first spiral track 34. This ensures the head 20will cross over the first spiral track 34 when writing the second spiraltrack 32 as illustrated in FIG. 3. In the example of FIG. 3, the secondspiral track 32 is written at a higher radial velocity than the firstspiral track 34 such that the slope of the second spiral track 32 isgreater than the slope of the first spiral track 34. In anotherembodiment, the second spiral track 32 may be written at a lower radialvelocity than the first spiral track 34.

FIG. 4A illustrates an embodiment wherein the first spiral track 18comprises a periodic pattern written at a first frequency (periodicallyinterrupted by a sync mark), and the second spiral track 24 comprises aperiodic pattern written at a second frequency (periodically interruptedby a sync mark) different from the first frequency. This embodiment mayhelp attenuate crosstalk in the read signal generated while reading thefirst spiral track 18 while simultaneously writing the second spiraltrack 24. In one embodiment, the control circuitry may filter the readsignal generated while reading the first spiral track 18 based on thefrequency of the periodic pattern in the first spiral track 18. FIG. 4Billustrates an example of this embodiment wherein the control circuitrymay bandpass filter the read signal to extract the frequency componentin the read signal corresponding to the periodic pattern in the firstspiral track 18.

In the example of FIGS. 4A and 4B, the periodic pattern in the firstspiral track 18 comprises a lower frequency than the periodic pattern inthe second spiral track 24. However, in other embodiments the periodicpattern in the first spiral track 18 may comprise a higher frequencythan the periodic pattern in the second spiral track 24. Any suitabledelta between the frequencies may be employed, and in one embodiment thefrequencies and the delta are selected to reduce the implementation costand complexity of the bandpass filter.

In the embodiment of FIG. 2C, the second spiral track 24 is writtencontinuously so as to eventually overwrite the first spiral track 18 asthe write element 28 passes over the first spiral track 18. Thisembodiment may improve performance while servoing on the second spiraltrack 24 since in one embodiment there are no gaps (or a reduced numberof gaps) in the second spiral track 24. In one embodiment, when readingthe second spiral track 24, for example to servo the head 20 over thedisk surface 16 while writing servo sectors of concentric servo tracks,the resulting read signal may be filtered based on the frequency of theperiodic pattern in the second spiral track 24. For example, the readsignal may be bandpass filtered so as to extract the frequency componentcorresponding to the second spiral track 24, thereby attenuatinginterference from the periodic pattern in the first spiral track 18 nearthe locations where the second spiral track 24 overwrites the firstspiral track 18.

FIG. 5A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a disk surface 16 comprising afirst spiral track 18 at least partially overwritten by a second spiraltrack 24. The disk drive further comprises control circuitry 22configured to execute the flow diagram of FIG. 5B, wherein a head 20 isactuated over the disk surface 16 based on the second spiral track 24(block 35).

FIGS. 5A and 5C illustrates an example embodiment wherein the secondspiral track 24 is written in an opposite radial direction as the firstspiral track 18 similar to the embodiment described above with referenceto FIG. 2C. In one embodiment, the control circuitry 22 servos the head20 in a substantially concentric path 36, for example, while writingconcentric servo sectors to the disk such as shown in FIG. 1. Asillustrated in FIG. 5C, the read element 26 may pass over the secondspiral track 24 at a radial location where the second spiral track 24overwrites the first spiral track 18, and therefore there may beinterference in the read signal due to reading at least part of thefirst spiral track 18. This interference may reduce the accuracy of theresulting position signal generated based on demodulating the secondspiral track 24. Accordingly, in order to reduce this interference, inone embodiment the first spiral track 18 comprises a periodic patternwritten at a first frequency, and the second spiral track 24 comprises aperiodic pattern written at a second frequency different from the firstfrequency. In the embodiment shown in FIG. 5C, the second frequency ishigher than the first frequency; however in another embodiment thesecond frequency may be lower than the first frequency.

In one embodiment, the second spiral track 24 may be demodulated byprocessing the read signal samples to compute a discrete Fouriertransform (DFT) at the second frequency using any suitable technique.When demodulating the second spiral track 24 using a DFT, theinterference from the first spiral track 18 may be attenuated when theratio between the second frequency and the first frequency issubstantially an integer plus one-half as shown in FIG. 6. The ratio maybe inverted in the embodiment where the second frequency is lower thanthe first frequency (i.e., the interference from the first spiral track18 may be attenuated when the ratio between the first frequency and thesecond frequency is substantially an integer plus one-half). In anotherembodiment shown in FIG. 7, the control circuitry 22 may bandpass filterthe read signal proximate the second frequency, thereby attenuatinginterference from the first spiral track 18. The bandpass filtering maybe implemented in any suitable manner, including in the analog domainand/or in the digital domain.

In the embodiment of FIG. 4A, the first spiral track 18 may comprise aperiodic pattern written at a first frequency as well as sync markswhich may facilitate demodulating the spiral track when writing thesecond spiral track 24. However, in one embodiment the sync marks in thefirst spiral track 18 may interfere with the demodulation of the secondspiral track 24 when attempting to servo on the second spiral track 24(e.g., when writing concentric servo sectors). This embodiment isillustrated in FIG. 8A wherein the frequency spectrum of the firstspiral track 18 may comprise a peak at the frequency of the periodicpattern, as well as a frequency component 38 due to the sync marks thatmay overlap with the peak frequency component of the second spiral track24. Accordingly, in one embodiment illustrated in FIG. 8B the firstspiral track 18 may be written without sync marks (i.e., consistprimarily of the periodic pattern written at the first frequency),thereby avoiding the interference when demodulating the second spiraltrack 24 by removing the frequency component as illustrated in FIG. 8C.In one embodiment, the first spiral track 18 may be demodulated usingother techniques not based on sync marks. For example, the first spiraltrack 18 may be demodulated by evaluating a peak in the read signalgenerated when reading the first spiral track 18.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a disk controller, or certainoperations described above may be performed by a read channel and othersby a disk controller. In one embodiment, the read channel and diskcontroller are implemented as separate integrated circuits, and in analternative embodiment they are fabricated into a single integratedcircuit or system on a chip (SOC). In addition, the control circuitrymay include a suitable preamp circuit implemented as a separateintegrated circuit, integrated into the read channel or disk controllercircuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In another embodiment, the instructions are stored on the diskand read into a volatile semiconductor memory when the disk drive ispowered on. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry.

While the above examples concern a disk drive, the various embodimentsare not limited to a disk drive and can be applied to other data storagedevices and systems, such as magnetic tape drives, solid state drives,hybrid drives, etc. In addition, some embodiments may include electronicdevices such as computing devices, data server devices, media contentstorage devices, etc. that comprise the storage media and/or controlcircuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device comprising: a disk surfacecomprising a first spiral track at least partially overwritten by asecond spiral track; a head actuated over the disk surface; and controlcircuitry configured to servo the head over the disk surface based onthe second spiral track; wherein: the first spiral track comprises aperiodic pattern written at a first frequency; and the second spiraltrack comprises a periodic pattern written at a second frequencydifferent from the first frequency.
 2. The data storage device asrecited in claim 1, wherein a ratio between the first frequency and thesecond frequency is substantially an integer plus one-half.
 3. The datastorage device as recited in claim 1, wherein a ratio between the secondfrequency and the first frequency is substantially an integer plusone-half.
 4. The data storage device as recited in claim 1, wherein thecontrol circuitry is further configured to: generate a read signal whilereading the second spiral track; and filter the read signal based on thesecond frequency to attenuate crosstalk caused by the first spiraltrack.
 5. The data storage device as recited in claim 4, wherein thecontrol circuitry is further configured to bandpass filter the readsignal proximate the second frequency.
 6. The data storage device asrecited in claim 4, wherein: the first spiral track consists of thefirst periodic pattern; and the second spiral track comprises a syncmark periodically interrupting the second periodic pattern.
 7. The datastorage device as recited in claim 1, wherein: the first spiral trackconsists of the first periodic pattern; and the second spiral trackcomprises a sync mark periodically interrupting the second periodicpattern.
 8. A method of operating a data storage device, the methodcomprising servoing a head over a disk surface based on a second spiraltrack on the disk surface, wherein: a first spiral track on the disksurface is at least partially overwritten by the second spiral track;the first spiral track comprises a periodic pattern written at a firstfrequency; and the second spiral track comprises a periodic patternwritten at a second frequency different from the first frequency.
 9. Themethod as recited in claim 8, wherein a ratio between the firstfrequency and the second frequency is substantially an integer plusone-half.
 10. The method as recited in claim 8, wherein a ratio betweenthe second frequency and the first frequency is substantially an integerplus one-half.
 11. The method as recited in claim 8, further comprising:generating a read signal while reading the second spiral track; andfiltering the read signal based on the second frequency to attenuatecrosstalk caused by the first spiral track.
 12. The method as recited inclaim 11, further comprising bandpass filtering the read signalproximate the second frequency.
 13. The method as recited in claim 11,wherein: the first spiral track consists of the first periodic pattern;and the second spiral track comprises a sync mark periodicallyinterrupting the second periodic pattern.
 14. The method as recited inclaim 8, wherein: the first spiral track consists of the first periodicpattern; and the second spiral track comprises a sync mark periodicallyinterrupting the second periodic pattern.